A drill ship or a liquefied natural gas-floating production storage and offloading (LNG-FPSO) for drilling of gas or oil in a seabed includes a turret to assist the drilling. The turret is often installed in a vertical opening or a moon pool provided at one end, typically the bow, of a vessel, and is moored by being fixed to a subsea well platform by chains or the like.
Also, the turret is installed in a vessel to allow the vessel to relatively rotate around a center axis of the turret and to provide a stable and continuous transfer path of gas or oil from the subsea well platform to the vessel during a drilling operation. In other words, even when a vessel on a sea surface is moved by wind, waves, or tides during transferring gas or oil, the vessel may freely rotate around the fixed turret as a center axis. Accordingly, the gas or oil may be stably transferred through a tube inside the fixed turret regardless of the movements of the vessel.
In a structure to allow the vessel to rotate around the turret, for example, a bearing provided on the turret slidably contacts an inner wall of a hull forming a vertical opening. In this case, the inner wall of a hull contacting the bearing requires strength enough to endure a horizontal load applied during the sliding with the turret.
To satisfy the required strength, conventionally, Inconel welling is performed on the entire surface of the inner wall of a hull that contacts the bearing and a bearing contact surface is formed through a grinding process. However, such a conventional method is disadvantageous because of an excessive welling work to form an Inconel welling bead, defective welding precision according thereto, and difficulty in mechanical processing, by which a considerable work time is consumed and production efficiency is deteriorated.